Attenuator network



July 21, 1959 WUNDERMAN 2,896,086

ATTENUATOR NETWORK FiledJuly 1, 1957 F 1 l3 E LIGHT DEAM nor/av F l E E INVENTOR.

/rw/'n Wunaerman l /5 ATTOR/VE Y5 United States Patent Ofiice 2,896,086 Patented July 21, 1 959 ATIENUATOR NETWORK Irwin Wunderman, Mountain View, Calif., assignor to Hewlett-Packard Company, Palo Alto, Calili, a corporation of California Application July 1, 1957, Serial No. 669,149

Claims. (Cl. 250-211) This invention relates generally to an attenuator network and more particularly to a photoresistive attenuator network.

As is well known, attenuator networks are employed to introduce a known amount of loss when working with resistive impedances. In general, attenuator networks have input and output impedances which are suitably matched to the associated source and load irnpedances It is a general object of the present invention to provide an attenuator in which the attenuation and impedance may be optically controlled.

It is another object of the present invention to provide an attenuator network which includes a conductive grid network having a predetermined configuration which is covered by photoconductive material. The photoconductive material forms the resistive elements of the attenuator network. Light serves to vary the resistance of portions of the photoresistive material to give the desired attenuation and terminating impedances.

These and other objects of the invention will become more clearly apparent from the following description when taken in conjunction with the accompanying drawmg.

Referring to the drawing:

Figure 1 is a plan view of a suitable gridnetwork;

Figure 2 is a sectional view taken along the line 22 of Figure 1;

Figure 3 is a plan view showing a light pattern striking the photoconductive material;

Figure 4 shows an attenuator in which the light is controlled by means of a filter;

Figure 5 shows a plan view of a graded light filter which may be used in Figure 4;

Figure 6 shows an attenuator which is controlled by means of a light cam;

Figure 7 shows an attenuator which is controlled by the illumination from a pair of lights;

Figure 8 shows an attenuator in which the illumination is controlled by mechanical movement of the network; and

Figure 9 is an equivalent circuit diagram of an attenuator constructed in accordance with Figures 1 and 2.

The grid network 10 shown in Figure 1 comprises independent conductive grids 11, 12, 13 and 14 which are covered with a layer of photoconductive material, to be presently described. The grid 13 is interlaced with the grid 11 to form one of the optically controlled photoresistive elements of the attenuator, the grid 12 is interlaced with the grid 13 to form another optically controlled photoresistive element, and the grid 14 is interlaced with the grid 13 to form a third photoresistive element. The photoresistive elements, as illustrated, are connected to form an unbalanced T attenuator. An equivalent circuit is shown in Figure 9 wherein the resistors 16, 17 and 18 represent the photoresistive elements which form the T network. Each of the photoresistive elements is indicated as being variable, corresponding to the optical variation of resistance.

The grid network is covered with a layer of photoresistive material 15 (Figure 2) whereby adjacent grids are interconnected through the material. When the photoresistive material is dark, the resistance between grid elements is relatively high. With increasing illumination, the resistance is lowered an amount corresponding to the intensity and area of the illumination. The photoresistive material may be in the form of a powder which is dispersed in a binder and applied to the surface to form a relatively thin film. Alternatively, the powder may be dispersed in a carrier and applied to the grid network and the assembly is placed in an oven and baked at a relatively high temperature to form a sintered photoconductive layer.

Referring to Figure 3, the shaded area 19 represents a light beam which is impinging upon the photoconductive layer 15. The resistance of the layer interconnecting the grids 13 and 14 is lowered. The resistance 18 represents the resistance between these grids. Thus, with the light as shown, the resistance 18 is considerably lowered whereby maximum attenuation is obtained in the attenuator. As the light beam is moved to the left, the shunt resistance 18 is raised and the series resistances 16 and 17 are lowered. With the light illuminating the photoconductive material interconnecting the grids 11, 12 and 13, the shunt resistance is at its maximum and the series resistances 16 and 17 are at a minimum.. The attenuation introduced by the attenuator is at a minimum.

The geometry of the light pattern and the grid can be varied as desired to give the desired variation in resistance between the various elements to thereby control the input and output impedance as well as the attenuation introduced.

Referring to Figure 4, an alternative means for controlling the attenuation is shown. A light filter 21 is interposed between the light source 22 and the attenuating network 23. By moving the filter as indicated by the arrow 24, the illumination on various portions of the photoresistive material may be altered to control the resistance between the related grid elements. The filter 21 may be graded as shown in Figure 5 whereby a de-- sired variation of resistance with movement of the filter may be obtained.

In Figure 6 another means is shown for controlling the light incident upon the photoconductive material. An opaque shutter 2-6 having an optical cam 27 is moved as indicated by the arrow 28 between the light source and the material. In Figure 7 an opaque bafile 29 is interposed between a pair of lights 31 and 32 which may be independently controlled. By controlling the intensity of the lights 31 and 32, the attenuation and impedance of the attenuator network may be controlled. The attenuation may be controlled by moving the attenuator network. Thus, in Figure 8 the network is pivoted about the point 33.

The illumination may be electronically controlled by controlling the motion of the filter or shutter. Alternatively, one or more lights may be arranged whereby the attenuation can be controlled by controlling the power supplied to the light, as illustrated in Figure 7.

It is, of course, apparent that although a three terminal attenuator network has been described that other attenuator networks with more or less terminals may be constructed in accordance with the teaching of the invention.

It is seen that an attenuator is provided in which the resistance elements are optically controlled. The attenuation may be electronically controlled by electronically controlling the motion of the filter or shutter, or by controlling the intensity of the lights. The resistance may be mechanically controlled by moving the various elements as desired. The resistance arms of the attenuator network may be varied in accordance with any desired function by suitably, contouring the light cam, grading the filter or choosing the shape of the light beam.

I claim: I

1. A network comprising an interlaced grid network of conductive material, photoconductive material serv-g ing to interconnect the grids'of said network, said gridl network comprising four separate grids so disposed as to. form together with said photoconductive.material the resistive elements of a T-network, a light source, and means for controlling the light incident upon said photo-l conductive material whereby the attenuation and impedance level may be controlled as desired.

2. An attenuator network as in claim 1 wherein saidlight source emits a beam of predetermined pattern, and means are included for moving said beam relative to the interlaced grid network; V

3. An attenuator network as in claim 1 wherein said References Cited in the file of this patent UNITED STATES PATENTS 1,937,796 Smith et al. Dec. 5, 1933 2,643,297 Goldstein et al. June 23, 1953 2,674,154 Crandell Apr. 6, 1954 2,700,318 Snyder Jan. 25, 1955 2,768,310 Kazan et a1 Oct. 23, 1956 2,836,766 Halstead May 27, ,1958 2,856,589 Kazan Oct, 14,, 1958 

